The present invention relates to a breakerless ignition system with an automatic electronic advance circuit and particularly to such an ignition system in which advance changes over a wide range of speed, between a low speed retard timing and a high speed advance timing.
Ignition systems for internal combustion engines have been developed using solid state technology which eliminates the necessity of mechanical switching devices for establishing the properly timed firing pulse to the internal combustion engine. In the solid state system, a voltage sensitive transistor or other solid state switch responds to the ignition power supply, which is operated in synchronism with the engine. In many relatively small and low horsepower internal combustion engines, a magneto unit is the source of power for the ignition system. The output of the magneto unit is generally a periodic alternating current AC signal generated in synchronism with the engine operation. Thus, as the magnet moves past the winding the signal is generated which includes three half cycles which alternate about zero or reference level. The shape and configuration of the AC signal vary with speed, and in particular, the magnitude and frequency of the AC signal vary with speed. Generally, the leading and trailing portions of each signal have a lower amplitude than the central portion or half cycle. Further, the AC signal is synchronized with the rotation of the engine, such that the time position of the signal is directly related to the position of the piston and the desired firing cycle of the engine.
This phenomena is known and used to provide automatic changes in the angle of firing in the ignition system. Generally, the system is designed to provide a relative retard angle of firing at starting and low speeds. The firing angle advances with speed to provide optimum engine operation. For example, U.S. Pat. No. 3,504,373 which issued Mar. 31, 1970 provides a solid state ignition switch system which has an automatic advance with a firing just before the peak level is obtained. Other solid state ignition systems with various controls are shown in the following U.S. patents:
______________________________________ U.S. Pat. No. Issue Date Inventor ______________________________________ 3,504,373 03/31/1970 Strelow 3,938,491 02/17/1976 Mazza 4,130,101 12/19/1978 Jundt et al 4,178,892 12/18/1979 Podrapsky 4,233,951 11/18/1980 Take 4,452,199 06/05/1984 Andreasson ______________________________________
Although various solid state ignition systems have been disclosed, the cost and reliability, particularly with repeatability of system operation, have not been totally satisfactory. This is particularly true for the smaller internal combustion engines where the ignition system module is mounted in a relatively confined space and may be subjected to a wide range of temperatures during normal system operation. The modules are optimumly designed as small and highly compact modules which can be mounted in the system. Because of the wide temperature ranges encountered, the circuit must be typically stabilized to operate with a range of -40 degrees Fahrenheit (.degree.F.) to +200.degree. F. Further, the small engine market is highly competitive and minimizing of cost is a significant factor in producing a satisfactory competitive system.
The range of timing change is peferably from a relatively large angle of retard at starting and low engine speeds to an angle of advance at high normal operating speeds. The timing angle should therefore move from the descending or trailing side of the peak current signal at low engine speeds to the advance or leading side thereof at high engine speeds. Applicant does not know of an ignition system which provides a range beginning in a relatively extreme initial retard portion of the AC ignition signal and at high speed extending beyond the peak to a significant advance position, thereby producing the desirable wide change range of the timing angle.
Further, any system which is designed would necessarily demand a simple, compact construction at a competitive low cost, and producing a consistent, repeatable functioning with changes in speed.